It’s perhaps worth noting that the cleric can always turn multiple undead creatures. So if you had, say, a horde of zombies (separate creatures) rather than a swarm of death scarabs (one creature), you could still turn all of them if your turning check was high enough.
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KRyanOct 21 '13 at 14:12

I'm a bit unclear as to what the question is getting at. Is there a particular part of the swarm rules that you thought might make them immune to turning, or a particular part of the turning rules you thought might keep it from working on the swarm? Please elaborate.
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Matthew NajmonNov 8 '13 at 2:48

The first one. I believed that because of the undeads being a swarm, there maybe would be a chance that they would be unaffected by the turn. I never really got into the "use as one creature" rule of the swarms, but the answers got it cleared out :)
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Drunken_GuyNov 8 '13 at 7:01

4 Answers
4

Turning undead is a supernatural ability that a character can perform
as a standard action. It does not provoke attacks of opportunity.

You must present your holy symbol to turn undead. Turning is
considered an attack. You turn the closest turnable undead first, and
you can’t turn undead that are more than 60 feet away or that have
total cover relative to you. You don’t need line of sight to a target,
but you do need line of effect.

Just a minor fix: You referenced the pathfinder entry for turn undead, while I am using the dnd 3.5 tag. No biggie, just I tried to understand if I had it wrong with how it actually works all these years :P
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Drunken_GuyOct 21 '13 at 8:38

Assuming that nothing else prevents the cleric from turning a given swarm -for example, not having enough dice- the fact that it's a swarm won't prevent the cleric from turning it either.

A swarm is a single creature in D&D. The collective essentially takes on its own quasi-existence, independent of but coterminous with the creatures that comprise it: a hive-mind, collective unconscious, or whatever you want to call it. This single creature is what the cleric turns. The creatures that comprise the swarm (scarabs, in this case) merely follow the swarm, because that's what swarming creatures do: technically you haven't turned any one scarab, but because you turned the swarm, the scarabs act as if turned.

In theory you could use the mob rules to turn large groups of bigger creatures -say, an entire zombie horde- as a single creature, but the CR for something like that should probably be really, really high: best left to epic levels.

A swarm is a single creature, except when it's not. Any spell that has a finite number of targets (like Disintegrate) doesn't work on a swarm.
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TridusOct 22 '13 at 14:10

4

@Tridus Good point in the general case. In this case the finite number is HD and not targets, so for this case this answer is on-point and nicely clears up what appears to be the crux of confusion in the question.
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SevenSidedDie♦Oct 22 '13 at 16:25

Your monster have a HD that is not from each individual but from the swarm. That amount of scarabs together create the HD that your Cleric must turn.
You only have to make sure that the Cleric have the necessary level to turn that monster, changing the amount of scarabs that the swarm have.